Stony coral description

Porites corals form some of the largest of all coral colonies, with some reaching an incredible eight metres in height (3). The growth rate of Porites coral is very slow, perhaps only nine millimetres a year, therefore these giant colonies may be up to 1,000 years old, putting them among the oldest life forms on earth (3). Coral colonies are composed of many individual coral polyps, which are basically anemone-like animals that secrete a skeleton. The many polyps of a colony are joined together at the base of their skeletons (4). The colonies of Porites corals may form flat, branching, spherical or hemispherical structures; some hemispherical colonies may be over five meters across (4). The coral polyps possess tentacles which, in most species, are extended only at night, when they give the coral a furry appearance (3).

Related species

Stony coral biology

Like other reef-building corals, the polyps of Porites corals have microscopic algae (zooxanthellae) living within their tissues. Through photosynthesis, these symbiotic algae produce energy-rich molecules that the coral polyps can use as nutrition. In return, the coral provides the zooxanthellae with protection and access to sunlight (4). Poritescolonies also commonly house a wide variety of other fauna (4).

The majority of corals are hermaphrodite, and thus colonies possess both male and female reproductive organs. However, Porites corals have separate male and female colonies. With a few exceptions, fertilization is internal and therefore depends on free-swimming sperm from male colonies reaching the polyps of female colonies. The fertilised eggs then develop into larvae within the female polyp’s body cavity (3). When released, the larvae settle quickly close to the parent colony. Whilst this means that, unlike spawning corals, the coral is not easily dispersed, brooding corals have the advantage of their young settling in an environment that has already proved suitable for successful reproduction (4). Most of the spherical and hemispherical Porites species are tolerant of sedimentary environments, partly because they protect themselves with a thick film of mucous (4).

Stony coral status

Stony coral threats

Porites corals face the many threats that are impacting coral reefs globally. It is estimated that 20 percent of the world’s coral reefs have already been effectively destroyed and show no immediate prospects of recovery, and 24 percent of the world’s reefs are under imminent risk of collapse due to human pressures. These human impacts include poor land management practices that are releasing more sediment, nutrients and pollutants into the oceans and stressing the fragile reef ecosystem. Over fishing has ‘knock-on’ effects that results in the increase of macro-algae that can out-compete and smother corals, and fishing using destructive methods physically devastates the reef. A further potential threat is the increase of coral bleaching events, as a result of global climate change (5). The predatory starfish, Acanthaster planci, or ‘crown-of-thorns starfish’, feeds on a wide range of coral species. For little understood reasons, outbreaks of this starfish occur at regular intervals, and large numbers of starfish can have devastating effects on the reef. They can eat so much that they can kill most of the living coral in a region, which may take the reef up to fifteen years to fully recover (6). Due to the exceptionally slow growth rate of Porites corals, these species may not be able to fully recover in the time before the next starfish outbreak, and thus may be sent into a period of prolonged decline (7).

An additional potential threat arises from collection for the coral trade. Porites is one of four genera that constitute the majority of the dead coral trade, for ornaments and jewellery. Live Porites are also collected at a lower level for the aquarium industry, and has previously been traded for biomedical purposes. This trade, which probably supplied a specialised market for the use of coral in bone grafts, peaked in 1992 but has since declined to extremely low levels (8).

Stony coral conservation

Porites corals are listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), which means that trade in this species should be carefully regulated (2). Indonesia and Fiji have export quotas for Porites corals (2). Porites corals will form part of the marine community in many marine protected areas (MPAs), which offer coral reefs a degree of protection, and there are many calls from non-governmental organisations for larger MPAs to ensure the persistence of these unique and fascinating ecosystems (5).

Authentication

Glossary

Relating to corals: corals composed of numerous genetically identical individuals (also referred to as zooids or polyps), which are produced by budding and remain physiologically connected.

Larvae

Relating to corals: the stages of development before settlement on the reef. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.

Photosynthesis

Metabolic process characteristic of plants in which carbon dioxide is broken down, using energy from sunlight absorbed by the green pigment chlorophyll. Organic compounds are produced and oxygen is given off as a by-product.

Polyp

Typically sedentary soft-bodied component of Cnidaria (corals, sea pens etc), which comprise of a trunk that is fixed at the base; the mouth is placed at the opposite end of the trunk, and is surrounded by tentacles.

Spawning

Relating to corals: the release of eggs and sperm into the water, where fertilization takes place externally.

Symbiotic

A relationship in which two organisms form a close association, the term is now usually used only for associations that benefit both organisms (a mutualism).

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